For example, during trans-aortic valve implantation (TAVI) procedures, the positioning of the valve prosthesis is an important task. The correct positioning, for example, may be beneficial in order to minimize paravalvular aortic leaks, which may affect future heart performance. The exact positioning of the valve may be determined during the planning stage by an interventionist to ensure that the coronary ostia will not be obstructed and to minimize the risk of paravalvular aortic leaks. In other words, the correct positioning is aimed to get the best possible outcome of the procedure. As an example, US 2011/0096969A1 relates to a method and system for shape constraint aortic valve landmark detection. The landmark detection is provided using 3D medical images. However, it has been shown that the determination requires 3D medical images and can thus be cumbersome. The detected landmarks may then be used for the positioning of a valve prosthesis.